Abstract
BackgroundWaterlogging is one of the most serious abiotic stresses affecting wheat-growing regions in China. Considerable differences in waterlogging tolerance have been found among different wheat varieties, and the mechanisms governing the waterlogging tolerance of wheat seeds during germination have not been elucidated.ResultsThe results showed no significant difference between the germination rate of ‘Bainong 207’ (BN207) (after 72 h of waterlogging treatment) and that of the control seeds. However, the degree of emulsification and the degradation rate of endosperm cells under waterlogging stress were higher than those obtained with the control treatment, and the number of amyloplasts in the endosperm was significantly reduced by waterlogging. Transcriptomic data were obtained from seed samples (a total of 18 samples) of three wheat varieties, ‘Zhoumai 22’ (ZM22), BN207 and ‘Bainong 607’ (BN607), subjected to the waterlogging and control treatments. A comprehensive analysis identified a total of 2775 differentially expressed genes (DEGs). In addition, an analysis of the correlations among the expression difference levels of DEGs and the seed germination rates of the three wheat varieties under waterlogging stress revealed that the relative expression levels of 563 and 398 genes were positively and negatively correlated with the germination rate of the wheat seeds, respectively. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses showed that the difference in the waterlogging tolerance among the three wheat varieties was related to the abundance of key genes involved in the glycolysis pathway, the starch and sucrose metabolism pathway, and the lactose metabolism pathway. The alcohol dehydrogenase (ADH) gene in the endosperm of BN607 was induced immediately after short-term waterlogging, and the energy provided by the glycolysis pathway enabled the BN607 seeds to germinate as early as possible; in addition, the expression of the AP2/ERF transcription factor was upregulated to further enhance the waterlogging tolerance of this cultivar.ConclusionsTaken together, the results of this study help elucidate the mechanisms through which different wheat varieties respond to waterlogging stress during germination.
Highlights
Waterlogging is one of the most serious abiotic stresses affecting wheat-growing regions in China
We found that the transcriptional levels of ADH2 (TraesCS5D02G196300) and ADH3 (TraesCS4B02G106400) (Fig. 7) after 72 h of the waterlogging treatment were lower than those obtained with the control treatment, and the greatest decrease was observed in Zhoumai 22 (ZM22), followed by Bainong 207’ (BN207) and Bainong 607’ (BN607)
This study revealed that the expression difference levels of six WRKY transcription factors gradually decreased in ZM22, BN206 and BN607 (Table 1), which indicated that the germination of ZM22, BN207 and BN607 seeds under the waterlogging treatment was negatively regulated by WRKY transcription factors
Summary
Waterlogging is one of the most serious abiotic stresses affecting wheat-growing regions in China. Irrigation practices and/or poor soil drainage, waterlogging annually affects large areas of farmlands worldwide, and these effects result in anoxic (absence of O2) soils and severe hypoxia or anoxia within crop roots. Relevant studies have shown that waterlogging might affect the hormone content in wheat roots and stems, possibly by impacting the production of ethylene [3], and reduce the absorption of mineral nutrients by plant roots [4]. The uneven terrain or poor drainage systems of farmlands cause waterlogging in the soil, which often leads to a lack of oxygen supply to the soil and the inhibition of seed germination, and these effects reduce the germination rate (GR) of wheat [7] and result in reductions in wheat production
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